This invention relates to liquid-vapour contact apparatus. The term `vapour` as used herein includes `gas` within its scope and vice versa.
U.S. Pat. No. 5,091,119 relates to a liquid-gas contact device comprising: a liquid-gas contact tray having a liquid-bearing surface along which in use liquid is able to flow from a liquid receiving edge of the liquid bearing surface to an opposed liquid outlet edge thereof, a multiplicity of elongate apertures in the tray for the passage of gas from below to above the tray, each aperture having a gas deflector associated therewith and being so disposed as to impart to the gas a component of velocity in a direction toward the liquid outlet edge, and at least several liquid flow impedance members overlying the liquid-bearing surface between said liquid receiving edge and said outlet edge, the deflectors and flow impedance members having a height such that in operation of the device they are fully submerged in the liquid flowing thereacross. The tray preferably comprises a sheet of expanded metal. Preferably, the liquid flow impedance members are provided by a second sheet of expanded metal overlying the tray. The mesh size of the second sheet is greater than that of the first sheet. The first sheet of expanded metal typically has a percentage open area in the range of 20 to 30%. The liquid-gas contact device is particularly suitable for use as a distillation tray in for example the separation of air. In comparison with conventional distillation trays, it causes a relatively small pressure drop. Moreover, the liquid-gas contact device has good `turndown` characteristics. That is to say it is capable of operating at high efficiency over a range of different gas flow rates (and hence gas velocities).
The maximum gas velocity at which such liquid-gas contact devices can be used efficiently is limited by a tendency for the vapour flowing vertically upwards from one tray to the next to carry liquid with it onto the next tray. Accordingly, if the liquid-vapour contact is performed as part of a distillation process, the ascending vapour becomes effectively enriched in a less volatile component of the mixture being distilled with the result that the separation is rendered less complete.
It is an aim of the present invention to provide an apparatus that ameliorates this problem.